she could be doing this to get your attention as there may be something wrong with her, our cat did similar, id suggest taking her to a vet to get a check up to see if alls fine
http://www.ebay.com/itm/100-G-Aquarium-Reef-RO-DI-5stage-Reverse-Osmosis-Water-/180544571860?pt=LH_DefaultDomain_0&hash=item2a094b89d4#ht_9496wt_1110
this is better and has di resin all up would be about $260 NZ
how about something like this?
http://www.ebay.com/itm/Countertop-150-GPD-Reverse-Osmosis-RO-system-get-pure-water-6-25-gallone-Hour-/110750138786?pt=LH_DefaultDomain_0&hash=item19c93901a2
NZD $159
or this
http://www.ebay.com/itm/50-GPD-Drinking-RO-Reverse-Osmosis-System-ROH-5-50-/110500308941?pt=Small_Kitchen_Appliances_US&hash=item19ba54e7cd#ht_8182wt_1110
NZD $230